Big orchestral sound in pop, rock etc.

David Byrne "Live From Austin, TX"

Elton John "Elton John"

Collective Soul "Home: A Live Concert Recording with the Atlanta Symphony Youth Orchestra"

Any thing by Electric Light Orchestra 

Early albums by the Moody Blues 

Rick Wakeman "The Six Wives of Henry VIII"

King Crimson "In The Court of the Crimson King"

Look no further than almost the entire genre, and most of its subgenres, of progressive music.

In the 70’s, the vast majority of these bands, had a big orchestral sound. Mostly due to the use of the keyboards available at the time. Hammond organ, Mellotron (an instrument that used analog tapes of massed strings, choir, horns, flutes), String Ensemble, various synths, etc.

You already listed Procol Harum, who are sometimes considered a prog band, so you are partway there.

I could list pages of bands and albums to look for.

Yes - Close to the Edge

King Crimson - Larks’ Tongues in Aspic, Starless and Bible Black, In the Court of the Crimson King, In the Wake of King Poseidon

Genesis - Foxtrot, Nursery Crime, The Lamb Lies Down on Broadway, Wind and Wuthering

Premiata Forneria Marconi (PFM) - Storia di un Minuto, Per Un Amico, The World Became the World

Le Orme - Felona e Sorona

And from more recently than the 70’s:

Amglagard - Hybris, Epilog, Viljans Öga

The flower Kings - Stardust We Are, Unfolding the Future

Hostsonaten - Springsong, Winterthru, Autumsymphony, Summereve

And if you are in the avant-gard mood. Still big and symphonic sounding, but atonal, and ’thorny’ sounding.

Univers Zero - Heresie. Clivages, Implosion

Art Zoyd - Symphonie Pour Le Jour Où Brûleront Les Cités, Berlin, Génération Sans Futur

This is just a very short tlist.

I'll throw in:

Santana - Santana

Tower of Power - Back to Oakland

M

Joni Mitchel, Miles of Isles

- Pet Sounds by The Beach Boys.

- Randy Newman's debut album is heavily orchestrated, but he is far from a Rock band.

- Phil Spector's 1960's productions feature a large ensemble (often three bassists, two pianists, up to four guitarists, numerous string and brass players).

- On their Rock Of Ages live album The Band augmented their 5-piece line-up with a great horn section, the charts written by Alan Toussaint.